Liwei Lin (Advisor)

Research Advised by Professor Liwei Lin

Lin Group:  List of Projects | List of Researchers

High-Aspect-Ratio Three-Dimensional Electrospinning via a Tip Guiding Electrode

Gaofeng Zheng
Jiaxin Jiang
Xiang Wang
Wenwang Li
Zhaojie Yu
Liwei Lin
2021

Electrospinning setup with a sharp tip guiding electrode has been designed for high-aspect-ratio three-dimensional (3D) electrospinning by enhancing the electrical field strength to guide nanofibers toward designated paths layer by layer. This setup helps to deposit nanofibers under a steady charge transfer process and overcomes the electrical interferences. The polymer jet via the electrohydrodynamic process has been used to direct-write ordered, 3D structures with the aspect-ratio (height/width) up to 25 for various patterns, such as rectangular grids and five-point stars....

Electrohydrodynamic 3D Printing of Orderly Carbon/Nickel Composite Network as Supercapacitor Electrodes

Bing Zhang
Jiangkang He
Gaofeng Zheng
Yuanyuan Huang
Chaohung Wang
Peisheng He
Fanping Sui
Lingchua Mueng
Liwei Lin
2021

Electrohydrodynamic (EHD) 3D printing of carbon-based materials in the form of orderly networks can have various applications. In this work, microscale carbon/nickel (C-Ni) composite electrodes with controlled porosity have been utilized in electrochemical energy storage of supercapacitors. Polyacrylonitrile (PAN) was chosen as the basic material for its excellent carbonization performance and EHD printing property. Nickel nitrate (Ni(NO3)2) was incorporated to form Ni nanoparticles which can improve the conductivity and the capacitance performance of the electrode. Well-aligned PAN-Ni(NO3...

A 36-Channel Auto-Calibrated Front-End ASIC for a pMUT-Based Miniaturized 3-D Ultrasound System

Jihee Lee
Kyoung-Rog Lee
Benjamin E. Eovino
Jeong Hoan Park
Luna Yue Liang
Liwei Lin
Hoi-Jun Yoo
Jerald Yoo
2021

We present an area- and power-efficient application-specific integrated circuit (ASIC) for a miniaturized 3-D ultrasound system. The ASIC is designed to transmit pulse and receive echo through a 36-channel 2-D piezoelectric Micromachined Ultrasound Transducer (pMUT) array. The 36-channel ASIC integrates a transmitter (TX), a receiver (RX), and an analog-to-digital converter (ADC) within the 250-μm pitch channel while consuming low-power and supporting calibration to compensate for the process variation of the pMUT. The charge-recycling high-voltage TX (CRHV-TX) in standard CMOS...

Electrically Adaptive and Shape-Changeable Invertible Microlens

Jin Woo Bae
Dong-Soo Choi
In-Ho Yun
Dong-Heon Han
Seung Ju Oh
Tae-Hoon Kim
Jeong Ho Cho
Liwei Lin
Sang-Youn Kim
2021

Existing soft actuators for adaptive microlenses suffer from high required input voltage, optical loss, liquid loss, and the need for assistant systems. In this study, we fabricate a polyvinyl chloride-based gel using a new synergistic plasticization method to achieve simultaneously a high optical transparency and an ultrasoft rubber-like elastic behavior with a large voltage-induced deformation under a weak electric field. By compressing the smooth gel between two sets of annular electrodes, a self-contained biconvex microlens is realized that is capable of considerable shape changes in...

Improved Ring-Down Time and Axial Resolutions of PMUTs via Phase-Shift Excitation Scheme

Sedat Pala
Zhichun Shao
Yande Peng
Liwei Lin
2021

We have proposed a phase-shift cancellation scheme to reduce the ring down period of ultrasonic transducers and increase axial resolutions. A piezoelectric micromachined ultrasonic transducer (pMUT) consisting of 80 elements with circular diaphragms of 415 μm in radius made of 2 μm-thick AlN layer has a measured resonant frequency of 160 kHz. The ring down period is minimized by emitting ten pulses followed by six additional pulses with a 180° phase difference. Results show the ring down period is shortened by 13% and 7.5% for a single element and the 80-element array, respectively. In...

Ultrasound-Induced Haptic Sensations via PMUTs

Sedat Pala
Zhichun Shao
Yande Peng
Liwei Lin
2021

This work presents the sense of touch via non-contact ultrasonic waves by a dual-electrode bimorph piezoelectric micromachined transducer (pMUT) array. The prototype device has 12×12 elements with circular diaphragms of 415μm in radius made of 2μm-thick AlN. They are fabricated by a CMOS compatible micromachining process resulting a resonant frequency at 109.4kHz. Experimentally, a best haptic sensation on human fingers is found when emitting high frequency ultrasonic waves to emulate 100Hz signals by means of pulse width modulation with a 50% duty cycle. Strong haptic sensations are...

Ultrasound Induced Haptic Sensation by pMUTs

Sedat Pala
2021
Spring 2021 BSAC Research Review Presentation View Slides(link is external) View Presentation(link is external)

Piezoelectric Micromachined Ultrasonic Transducers With Pinned Boundary Structure

Yue Liang
Benjamin Eovino
Liwei Lin
2020

This paper reports the approach to boost the acoustic performances of PMUTs (Piezoelectric Micromachined Ultrasonic Transducers) including vibrational amplitude, acoustic pressure and electromechanical coupling by using the pinning boundary structure. An analytical model is developed based on an assumed mode shape and is validated with matching results from numerical simulations. Prototyped devices are fabricated and tested with a measured 2.5X improvement in displacement and 3.5X higher pressure output per volt at resonance as compared to those of PMUTs with clamped boundary. As a...

BPN934: Display Compatible pMUTs

Sedat Pala
2020

Ultrasonic transducers have been used in many applications from medical imaging to range finding. In recent years, applications have been further expanded to hand-held devices such as fingerprint sensors, and gesture recognitions thanks to advancements in micromachined ultrasonic transducers (MUTs). Compared to conventional ultrasound devices, MEMS ultrasonic transducers have advantages of higher resolution, higher bandwidth, and lower power consumption. More recently, products to interact electronic devices from a distance have been introduced. These products either require an allocated...

BPN917: Low-Cost, Efficient, Photolithography-Free Fabrication of Stretchable Electronics Systems on a Vinyl Cutter

Renxiao Xu
Peisheng He
2020

We present a new way for the fabrication of stretchable electronics systems without photolithography procedures by exploiting the through-cut, tunnel-cut, and blind-cut modes of a commercial desktop-size vinyl cutter. Compared to previous studies involving photolithography, our method produces a batch of representative devices in significantly reduced time (by ~69%) and cost (by ~73%) with similar feature sizes (100-1000um). Our inclusion of blind-cut and tunnel- cut modes facilitates the fabrication of complex stretchable electronics systems, rather than only electrodes and...